Method and system for monitoring the deformations of a tire in motion

ABSTRACT

A system for monitoring deformations of a moving tire mounted on a rim associated with a vehicle includes a moving station and a fixed station. The moving station is operatively coupled to the rim. The moving station measures, at least intermittently and in at least one direction, a distance between the moving station and an inner surface of the tire. The fixed station is operatively coupled to the vehicle. The fixed station receives from the moving station, at least intermittently, at least one first signal associated with the measurement. The moving station measures the distance within a time interval when a first antenna associated with the moving station and a second antenna associated with the fixed station are in proximity to each other. Related methods for monitoring deformations of a moving tire mounted on a rim associated with a vehicle are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage entry under 35 U.S.C. § 371 fromInternational Application No. PCT/EP00/12615, filed Dec. 12, 2000, inthe European Patent Office, the contents of which are relied upon andincorporated herein by reference; additionally, Applicants claim theright of priority under 35 U.S.C. § 119(a)-(d) based on patentapplication No. 99125692.6, filed Dec. 22, 1999, in the European PatentOffice; further, Applicants claim the benefit under 35 U.S.C. § 119(e)based on prior-filed, copending provisional application No. 60/173,553,filed Dec. 30, 1999, in the U.S. Patent and Trademark Office.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and system for monitoring thedeformations of a tyre in motion.

In particular, the present invention relates to the possibility ofdetermining the deformations of the carcassstructure of a tyre frominside the structure, for example in order to provide automaticintervention actuated or commanded by the driver, in the driving and/orcontrol system of the vehicle, to change the vehicle's behaviouraccording to measurements made on the tyre.

2. Description of the Related Art

There are known prior art devices for measuring characteristicparameters such as pressure and temperature inside a tyre.

Patent application EP 887211 describes a tyre monitoring systemcomprising a sensor which is positioned inside the tyre and is enabledto create an electrical impulse when the said sensor passes through thefootprint area formed by the contact of the tyre with the ground duringrolling. The system described in this patent also comprises means forfinding the ratio of the said electrical impulse to the duration of onerevolution of the tyre and means for transmitting the said ratio to aprocessing unit within the vehicle.

In particular, the sensor is placed within the tread of the tyre in sucha way that the said electrical impulse has a first peak at the entry ofthe sensor into the footprint area and a second peak at the exit fromthe footprint area.

According to the teaching of this patent, the ratio between the timeelapsed between the two peaks and the period of a complete revolutionmakes it possible to know the extent of flattening of the tyre duringthe travel of the vehicle.

This is because the sensor determines the instant of entry into thefootprint area and the instant of exit from the area. It is thuspossible to measure the length of this area, if the angular velocity ofthe tyre and its radius are known. The length of the footprint area isthen related to the flattening of the tyre, which is a criticalparameter of the tyre in operation, particularly in tyres for heavymotor transport.

Patent application EP 689950 describes a different method for monitoringparameters of a tyre such as its pressure and temperature. Inparticular, a self-powered programmable electronic device positioned onthe inner surface of a tyre or on its mounting rim is used. This devicecan be used to monitor and store the pressure, temperature and thenumber of rotations of the tyre, and may comprise an extensometer whoseoutput signal measures the bending of the inner surface of the tread, oran accelerometer which measures the value of the acceleration which thetread undergoes. Additionally, the device is activated by an externalradio-frequency signal and transmits an alarm signal if a predeterminedlimit of the measured values is exceeded.

There are also known methods for measuring deformations of the tread ofa tyre during motion and for transmitting it to a receiver located onthe vehicle.

Patent application WO 93.25400 describes a sensor, comprising a resonantcircuit which oscillates at a predetermined characteristic frequency,located within the tread of a tyre, and is capable of transmitting asignal directly dependent on the aforesaid deformations. This resonantfrequency is affected by the deformations of the tread during motion andthe sensor transmits electromagnetic waves proportional to thesevariations of the resonant frequency. These electromagnetic waves arereceived by a processing unit connected to a receiver located inside thevehicle.

U.S. Pat. No. 5,247,831 describes a method for monitoring the behaviourof the footprint area of a tyre during the travel of the vehicle tooptimize the driving of the vehicle. In particular, a piezoelectricsensor consisting of longitudinal strips of piezoresistive rubber isinserted into the tread. This sensor is capable of measuring thedeformations of the tread, since the strips change their electricalresistance as a function of the said deformations.

There are also known methods and devices for acting on the drivingand/or control system of the vehicle, particularly on the devices whichcontrol the suspension of the vehicle, to control its behaviouraccording to the information obtained from the axles of the vehicle orfrom the wheel hubs.

The publication “A method for the evaluation of the lateral stability ofvehicles and tires” by the Società Pneumatici Pirelli S.p.A., presentedat the International Automobile Tire Conference, Toronto, Canada, on 22Oct. 1974, illustrated a method for determining the dynamic behaviour ofthe vehicle as a function of the forces developed by the various typesof tyre sets and the various conditions of the road surface.

The publication principally cites three forces which determine thedynamic behaviour of a tyre, namely the vertical force, the longitudinalforce and the lateral force.

The vertical force is that which is due to the dynamic load to which thetyre is subjected. The longitudinal force is that which is due to themoment applied to the axis of the tyre as a result of an acceleration orbraking of the vehicle. The lateral force, also present in conditions ofnormal travel in rectilinear motion, is the resultant of the force dueto the characteristic angles of the vehicle suspension (camber andtoe-in) and to the ply-steer developed by the layers of inclined cordsof the belt structure of the tyre, and of the thrust generated by thecentrifugal force during drifting. The sum of the forces developed bythe four tyres generates a resultant system applied to the centre ofgravity of the vehicle, which balances the inertial forces anddetermines the attitude of the vehicle as a function of thecharacteristics of the suspension system of each axle. This resultantsystem is determined by means of suitable accelerometers, one positionedon the front axle and one on the rear axle of the vehicle. The articleshows a set of graphs showing the centripetal acceleration or thecentripetal force applied to the centre of gravity of the vehicle as afunction of the angle of slip of the corresponding axle. From graphsplotted for different ground conditions and different types of tyres, itis possible to determine the behaviour of the vehicle provided with apredetermined set of tyres and to determine any lateral slipping ofeither the front or the rear axle in cornering.

SUMMARY OF THE INVENTION

The applicant has observed that the aforesaid known systems ofcontrolling the behaviour of the vehicle is based on the system offorces measured at the hubs of the wheels, and the systems of measuringthe deformations of the tyre are based on the determination of thedeformations undergone by the tread in the footprint area of the tyre.

The applicant has observed that the values measured in these systemscannot be related in a biunique way to the conditions of travel of thetyre and, more precisely, to the system of forces developed by the tyrein each condition of travel.

The present invention is based on the applicant's perception that thedetermination of deformations of the tread, particularly in thefootprint area of the tyre, does not make it possible to identify thesystem of forces developed by the tyre or the deformations of the tyrecarcasswhich are associated with it and which represent the behaviour ofthe tyre. This behaviour is of considerable importance, especiallyduring certain particular events, such as the braking or acceleration ofthe vehicle, drifting, and variations of load on the tyre.

According to the above, the present invention originated from theapplicant's perception that the determination of the deformations of thetyre carcass, being related in a biunique way to the system of forcesdeveloped by the tyre in operation, makes it possible to determine thebehaviour of the tyre in any of its conditions of motion.

It has been found that the measurements of the deformation of thecarcassstructure of the tyre, at a given inflation pressure, accordingto a set of three Cartesian axes, in other words the deformation in thevertical direction, the deformation in the transverse direction and thedeformation in the longitudinal direction, correspond in a biunique way,or in any case a reproducible way, to the vertical, lateral andlongitudinal forces respectively which act on the tyre (or, in otherwords, to the forces which the tyre exchanges with the ground).

The applicant has previously described this technical solution and thedeterminations associated with it in patent application 99EP-114962.6,to which reference should be made for further and more detailedinformation, and which is to be understood as being integrallyincorporated in this description.

The present invention relates more specifically to a particular methodand a particular type of device for carrying out the aforesaiddeterminations.

In particular, the applicant has discovered a method for determining thedeformations of a tyre in motion, which consists in measuring thesecharacteristic values within the tyre by means of a moving station whichsends a signal towards a point on the inner surface of the tyre,preferably when this point is within the footprint area of the tyre.This signal is reflected from the aforesaid surface and captured by themoving station which sends this reading to a fixed station located onboard the vehicle on which the tyre is fitted. The characteristics ofthe reflected signal are proportional to the distance between the pointof emission and the point of reflection.

The set of the determinations which are made measures the deformationsof the tyre in the aforesaid characteristic directions, in other wordsthe deformation in the vertical direction, the deformation in thetransverse direction and the deformation in the longitudinal direction.

In a first aspect, the present invention relates to a system formonitoring the deformations of a moving tyre fitted on a rim associatedwith a vehicle, characterized in that it comprises:

-   -   a moving station located in a predetermined position on the said        rim and capable of measuring in at least one direction the        distance between the said predetermined position and the inner        surface of the tyre,    -   a fixed station located on the said vehicle and capable of        receiving the said measurement from the said moving station.

Preferably, the said fixed station is capable of enabling the saidmeasurement made by the said moving station.

In particular, the said moving station comprises at least one sensorcapable of sending a signal within the tyre in a predetermineddirection, and of receiving the reflected signal.

In particular, the said sensor comprises an electronic circuit boardwith which are associated an optical beam emitting device, a first lens,an optical beam receiving device, and a second lens.

In particular, the said fixed station comprises a supporting element,fixed at one of its ends to a hub on which the said rim is mounted, andan electronic circuit board fixed to the said supporting element.

In particular, the said electronic circuit board of the fixed stationcomprises an oscillator circuit which supplies a drive circuit for afirst antenna, a radio-frequency receiver connected to the said firstantenna, and an electrical demodulator device connected to the saidradio-frequency receiver.

Preferably, the said fixed station is powered by the battery of thevehicle on which the tyre is fitted.

In particular, the said electronic circuit board of the sensor comprisesa second antenna, connected to a power supply unit, which supplies adrive circuit for the said optical beam emitter and a drive circuit forthe said optical beam receiver, and a circuit for reading the electricalsignal emitted by the said optical beam receiver.

Preferably, the said optical beam emitter comprises an LED.

Preferably, the said optical beam receiver comprises a pair of p-i-ndiodes.

In a second aspect, the present invention relates to a method formonitoring the deformations of a moving tyre fitted on a rim associatedwith a vehicle, characterized in that it comprises the following stages:

-   -   emitting a signal from a predetermined position on the said rim        in at least one predetermined direction within the tyre,    -   reflecting this signal from the inner surface of the tyre,    -   receiving this reflected signal,    -   processing the received signal in such a way as to generate a        processed signal proportional to the distance of the point of        reflection on the tyre from the said predetermined position in        the said at least one predetermined direction.

In particular, the said stage of emitting a signal comprises:

-   -   enabling a moving station located on the said rim to emit the        said signal when the said moving station passes through the        footprint area of the tyre.

Preferably, the said method additionally comprises the stage oftransferring the said signal processed by the said moving station to afixed station located on the said vehicle.

Preferably, the said stage of enabling a moving station is carried outby the said fixed station.

Preferably, the said stage of enabling the moving station comprises thestage of supplying power to the moving station for a time intervalduring which the stage of transferring the processed signal from thesaid moving station to the said fixed station is also carried out.

In particular, the said stage of enabling a moving station comprises thestage of generating a magnetic field at the said fixed station in thedirection of the said moving station and of supplying power by means ofthe said magnetic field to a drive circuit in the said moving stationfor an optical beam emitter.

Preferably, the said stage of transferring the said processed signalfrom the said moving station to the said fixed station comprises thestages of:

-   -   generating a magnetic field corresponding to the said processed        signal at the said moving station in the direction of the said        fixed station,    -   converting the said magnetic field to an electrical signal,    -   decoding the said electrical signal in such a way that the        corresponding processed signal is obtained.

In a further aspect, the present invention relates to a wheel forvehicles, comprising a tyre fitted on a supporting rim, characterized inthat it comprises a moving station located at a predetermined positionon the said rim and capable of measuring in at least one direction thedistance between the said predetermined position and the inner surfaceof the tyre, and capable of transmitting the said measurement to avehicle on which the said wheel is fitted.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention areexplained in greater detail in the following description, with referenceto the attached drawings, which are provided solely for explanatorypurposes and without any restrictive intent, and which show:

in FIG. 1, a cross section through a tyre fitted on its supporting rimunder a static load;

in FIG. 2, a detail of a pneumatic wheel showing the system fordetermining the deformations of the tyre according to the presentinvention, comprising a moving station and a fixed station;

in FIG. 3, a block diagram of the electronic circuit present within thefixed station shown in FIG. 2;

in FIG. 4, the moving station in detail, showing its electrical andoptical component parts;

in FIG. 5, a block diagram of the electronic circuit present within themoving station shown in FIG. 4;

in FIG. 6, a detail of the wheel according to the present invention,showing in particular the area of coupling between the antenna locatedon the fixed station and the antenna located in the moving station;

in FIGS. 7 a-b, an operational diagram of the optical measurement systemused by the moving station according to the invention;

in FIG. 8, a schematic representation of a pneumatic wheel;

in FIG. 9, a cross section through a tyre fitted on its supporting rim,showing a system according to the invention for monitoring thedeformation in the vertical direction (in other words the direction offlattening);

in FIG. 10, a longitudinal section through a tyre fitted on itssupporting rim in conditions of lateral drift, showing a systemaccording to the invention for monitoring the deformation in the lateraldirection (in other words the direction of lateral displacement);

in FIG. 11, a longitudinal section through a tyre fitted on itssupporting rim in conditions of braking, showing a system according tothe invention for monitoring the deformations in the longitudinaldirection (in other words the direction of longitudinal displacement);

in FIG. 12, the footprint area of the tyre, modified to a bean shape,during drifting, with the paths of the bead wires, the mid-line of thetread and a set of radial planes, showing for each of these thecorresponding value of deformation;

in FIG. 13, an example of a circuit diagram of the electronic circuitpresent within the fixed station;

in FIG. 14, an example of a circuit diagram of the electronic circuitpresent within the moving station.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows, by way of example, a wheel comprising a tyre 1, of thetype conventionally called “tubeless”, in other words without an innertube, and a supporting rim 2. This tyre 1 is inflated by means of aninflation valve 3 located, for example, in a known way, on the channelof the said rim.

The tyre 1 consists of an internally hollow toroidal structure formed bya plurality of components, and primarily by a textile or metalliccarcass, having two beads 5 and 5′ each formed along an innercircumferential edge of the carcass for securing the tyre to thecorresponding supporting rim 2. The said carcass comprises at least onepair of annular reinforcing cores, called bead wires 6 and 6′, which arecircumferentially inextensible and are inserted in the said beads(usually with at least one bead wire per bead).

The carcass comprises a supporting structure formed by a reinforcing ply4 which includes textile or metallic cords, extending axially from onebead to the other according to a toroidal profile, and which has each ofits ends associated with a corresponding bead wire.

In tyres of the type known as “radial”, the aforesaid cords lieessentially in planes containing the axis of rotation of the tyre.

On the crown of this carcass there is placed an annular structure 8,known as the belt structure, normally consisting of one or more stripsof rubberized fabric, wound on top of each other to form what is calleda “belt package”, and a tread 9 made from elastomeric material, woundaround the belt package, and stamped with a relief pattern for therolling contact of the tyre with the road. Two sidewalls 10 and 10′,made from elastomeric material, each extending outwards in the radialdirection from the outer edge of the corresponding bead, are also placedon the carcass, in lateral axially opposed positions.

In tyres of the type known as “tubeless”, the inner surface of thecarcass is normally covered with what is called a “liner” 111, in otherwords one or more layers of airtight elastomeric material. Finally, thecarcass may comprise other known elements, such as edges, strips andfillers, according to the specific design of the tyre.

The combination of all these elements determines the mechanicalcharacteristics of elasticity, rigidity and resistance to deformation ofthe tyre, which constitute the connection between the system of forcesapplied to the tyre and the extent of the corresponding deformationswhich it undergoes.

FIG. 2 shows, in a preferred embodiment of the invention, a system formonitoring the profile of the tyre of FIG. 1, fitted on the supportingrim 2 and associated with a vehicle; the system comprises a movingstation 30, fitted in the wall of the supporting rim 2 and including asensor/emitter 11 (called a “sensor” below for the sake of brevity),located within the cavity formed between the tyre and the rim,preferably along the mid-line plane of the said rim.

This moving station 30 comprises a transmitter which sends thedeterminations made to a fixed station 20, located on the said vehicleand provided with a suitable receiver.

The fixed station is preferably associated with the corresponding hub ofthe vehicle by means of suitable supports which are described below.

The moving station and the fixed station communicate with each other inany convenient way, for example by magnetic coupling between the twostations or by means of radio waves, preferably at high frequency.

In a preferred embodiment, the fixed station 20 comprises a supportingelement 21, fixed at one of its ends to the hub of a wheel, and anelectronic circuit board 22, placed preferably at the opposite end ofthe said supporting element, a block diagram of this circuit board beingprovided in FIG. 3.

In particular, the said electronic circuit board comprises an oscillatorcircuit 23, which supplies a drive circuit 24 for a first antenna 25,referred to below as the fixed antenna. The said circuit board alsocomprises a radio-frequency receiver 26 connected to the said antennaand an electrical demodulator device 27. The electrical power requiredto supply the said station can be provided directly by the vehiclebattery through a suitable drive circuit (not shown).

FIG. 13 shows an example of a circuit diagram of the electronic circuitboard of the fixed station 20. In particular, the oscillator 23,comprising a logic gate 231 and an oscillation frequency controlconsisting of a capacitor 232 and a variable resistor 233, is shown; thedrive circuit 24 of the antenna 25 comprising a squaring circuit 241consisting of flip-flops and a MOSFET amplifier 242 for the squaredsignal. The circuit also comprises the radio-frequency receiver 26 ofthe antenna signal, comprising a plurality of capacitance filters 261and a differential amplifier 262, and the electrical demodulator device27 comprising a suitable integrated component 271.

A person skilled in the art will note that this electrical circuit,shown in the block diagram in FIG. 3, can be constructed in any otherequivalent way, within the scope of the present invention, for exampleby changing the components from those shown in the diagram in FIG. 13.

In a preferred embodiment, the moving station 30 shown in FIG. 4essentially consists of the sensor 11, comprising a hollow support 12,preferably made from plastic material, into which an externally threadedtube 13 is inserted, preferably by screwing. The external thread 14 ofthe tube 13 is used both for inserting the tube into the support and forfixing the whole station within the wall of the supporting rim 2 of thewheel. Alternatively, the wall of the support can be threaded bothexternally, for fixing the station into the wall of the rim, andinternally, for enabling the tube 13 to be fitted. The main function ofthe support 12 is to form an airtight plug for sealing the hole formedin the body of the rim 2.

An electronic circuit board 15, with which are associated an opticalbeam emitting device 16, a first lens 17, an optical beam receivingdevice 18, and a second lens 19, is inserted into the tube 13.

The electronic circuit board 15, the block diagram of which is shown inFIG. 5, also comprises a second antenna 31, called the “moving antenna”below, connected to a power supply unit 32, which supplies theelectrical power to the optical beam emitting device 16 and to theoptical beam receiving device 18. For this purpose, the moving stationcomprises a drive circuit 33 for the said emitter 16 and a drive circuit35 for the said receiver 18. This electronic circuit board alsocomprises a circuit 37 for reading the signal received by the saidreceiver 18, the output of this circuit being connected to the saidmoving antenna 31.

Preferably, the optical beam emitting device 16 is an LED 34 which emitsan optical beam of infrared light.

Preferably, the optical beam receiving device 18 is formed by a pair ofp-i-n diodes P1 and P2 adjacent to each other.

FIG. 14 shows an example of a circuit diagram of the electronic circuitboard 15 of the moving station 30. In particular, it shows the powersupply 32, comprising a diode bridge 321 and a stabilizer circuit 322,the drive circuit 33 for the said LED 34, comprising a transistoramplifier 331, and the drive circuit 35 for the said p-i-n diodes P1 andP2, comprising an integrated stabilizer 351 and a load capacitor 352.The diagram also comprises the, circuit 37 for reading the signalreceived by the p-i-n diodes, comprising a differential amplifier 371,an oscillator 372, and a transistor amplifier 373 for amplifying thesignal received by the differential amplifier 371 and for sending it tothe antenna 31.

In this case also, a person skilled in the art will note that thiselectrical circuit, as defined by the block diagram in FIG. 5, can beconstructed in any other equivalent way, within the scope of the presentinvention, for example by changing the components from those shown inthe diagram in FIG. 14.

In the preferred example of embodiment described above, thecommunication between the said moving station and the said fixed stationis provided by means of magnetic coupling: in other words, the fixedantenna 25 and the moving antenna 31 preferably each comprise aninductive circuit, and the signal exchanged between the two antennae isa magnetic signal. In particular, with reference to FIG. 6, the fixedantenna 25 comprises a fixed coil 251, supplied with an alternatingradio-frequency current generated by the drive circuit 24, and themoving antenna 31 comprises a moving coil 311 which is integral with therim 2 of the wheel.

With each rotation of the pneumatic wheel, the moving coil 311 isbrought to a position facing the fixed coil 251, thus intercepting themagnetic field generated by the aforesaid coil. A correspondingelectrical voltage is induced in the moving coil 311 and supplies theenergy required for the operation of the moving station as a whole.

In an original way, according to the invention, the moving stationcarries out at least one of the specified determination in the tyrewithin the time interval during which the moving coil and the fixed coilare facing each other, and sends, by means of the moving coil, a signalcorresponding to the measurement which has been made. A voltagecorresponding to the measurement made is induced in the fixed coil, aswill be explained in greater detail below.

More precisely, the pair of antennae produce the transfer, between thefixed station and the moving station, of the electrical power requiredto supply the moving station, and also the transfer, between the fixedstation and the moving station, of the data on the measurements made inthe tyre. In particular, the information is transmitted in the form of asignal modulating the alternating power supply voltage of the fixedcoil.

Alternatively, the moving station can be supplied by a battery, in whichcase, preferably, the moving station also comprises an accelerometer orother equivalent device which switches off the station when the vehicleis stopped for a time exceeding a predetermined value, in order toeconomize on battery life.

Clearly, many other equivalent systems can also be used for the transferof the information.

In the embodiment described above, as has been said, the sensorcomprises both the signal emitting device and the element receiving thereflected signal. It should be understood that the two functions can becarried out by two independent elements which are separate from eachother, or by a single element which combines them both, according to thespecific technology used.

The signal emitted by the sensor 11 can be selected from a wide range oftypes of usable signals: preferably, those in the form of sound wavesare used, for example ultrasounds, or electromagnetic waves, which arereflected from the inner surface of the tyre. The reflection produced bythe inner surface of the tyre is particularly convenient, since it doesnot necessitate modifications to the structure of the tyre or to itsmanufacturing process, as it does not require additional reflectingelements or elements formed in the aforesaid surface.

The monitoring system described by way of example above operates in thefollowing way.

Within the fixed station 20, the coil 251 is supplied continuously withan electrical current generated by the oscillator 23 and made sinusoidalby the drive circuit 24, in such a way as to generate a magnetic field.

The moving coil 311 located in the moving station 30 intercepts thismagnetic field whenever the coil passes, during the rotation of thewheel, across the fixed coil. The interception of the magnetic fieldinduces a current in the moving coil. This current has the samesinusoidal form as the power supply current of the fixed coil and issent to the power supply device 32. This device preferably comprises, ina known way, a bridge of diodes or equivalent devices capable ofconverting a sinusoidal current to a continuous current. The currentproduced in this way supplies the optical beam emitting device and theoptical beam receiving device. In particular, this current supplies thedrive device 33 of the LED and the drive device 35 of the pair of p-i-ndiodes.

With reference to the diagram in FIGS. 7 a and 7 b, the optical beamemitting device (LED) emits an optical beam R collimated by the firstlens 17, directed towards a predetermined point of the surface of theliner, preferably selected within the footprint area of the tyre. Theray RR reflected from the surface L of the tyre liner reaches theoptical beam receiving device 18 (the pair of p-i-n diodes) at an angleof α dependent on the distance d of the surface of the liner from theemission point.

The optical beam receiving device comprises the second lens 19 and thepair of adjacent p-i-n diodes P1 and P2, as shown in FIG. 7 b. Theoptical beam collimated by the lens 19 is focused on these diodes. Asthe distance d between the surface of the liner and the lens 19 varies,the angle of the reflected ray RR changes and the surface area of thediodes struck by the optical beam changes as a result. In particular,there is a change in the ratio of the quantity of light incident on onediode to that incident on the other. This ratio is thereforeproportional to the distance between the lens and the surface whichproduces the reflection, in this case the surface of the liner.

In particular, in FIG. 7 a, s represents the distance between theposition (L) of the emitting device (LED) and the point (F) of arrivalof the reflected beam RR on the surface of the p-i-n diodes, brepresents the distance between the emitting device and the position ofthe lens 19, and d₁ represents the distance between the pair of p-i-ndiodes and the lens 19. Assuming that the distance d−d₀<<d, in otherwords that the variation of the distance d is very small with respect tothe initial value of the distance d, the following relation is true:d−d ₀=(s−s ₀)*d/b*d/d ₁  (1)and therefore:s−s ₀=(d−d ₀)/d*d ₁ /d*b  (2)

Each of the p-i-n diodes generates an electrical signal, the differencebetween which is proportional to the distance s−s₀ and therefore to thevariation of the distance d.

The device 37 for reading the electrical signal generated by the p-i-ndiodes determines this difference, and sends a corresponding electricalsignal via the antenna 31 to the fixed station. This signal transmissiontakes place because, in practice, the signal corresponding to theaforesaid difference carries out an amplitude modulation of thesinusoidal current induced in the moving coil. This amplitude modulationcreates a variation of magnetic field which is detected by the fixedcoil by means of the radio-frequency receiver 26. A signal correspondingto the aforesaid amplitude modulation is extracted from this coil bymeans of the demodulator 27 and is sent to the vehicle for the specifiedpurposes.

Now that the system of monitoring is known in a preferred embodiment ofits more general aspect, the method according to the invention forrecognizing the behaviour of a tyre in operation will be more clearlyevident.

FIG. 8 is a schematic representation of the structure of a pneumaticwheel with two springs m1 and m2 mounted in series between the hub M ofthe vehicle and the surface G of the ground.

The spring m1 represents the carcass structure of the tyre, while thespring m2 represents the structure of the tread, which has a specificelasticity dependent on the visco-elastic characteristics of the mixtureand on the geometrical characteristics of the tread design.

The force F applied to the footprint area of the tyre is balanced by anequal and opposite force F applied to the hub of the wheel. Unless thebehaviour of m1 (m2) is known, it is not possible to know the value ofthe deformation caused by the force acting on m1 (m2), and vice versa.

The forces transmitted by the tyre to the ground in a given situation,static or dynamic, are associated with the deformations of the tyre, inother words with the deviations of the profile of the carcass inoperation from the simple inflation profile of the carcass.

The profile of the carcass in operation is also defined here by the term“deformed state of the carcass”, while the simple inflation profile ofthe carcass, in other words that of the carcass in the tyre fitted onthe rim on which it is used and inflated to its nominal operatingpressure, in the absence of a load, is defined here, albeit incorrectly,as the equilibrium profile.

For the purposes of the present invention, the carcass profile isdefined as the profile according to the neutral axis of the carcassplies in the cross section of the tyre. In particular, the carcassprofile describes the deformed state of the said tyre under the effectof the system of forces acting on it.

It is not possible to deduce the deformed state of the carcass in aunique way from measurements made on the footprint area. Similarly, itis not possible to find the deformation of the footprint area in aunique way from the deformed state of the carcass, since the deformationdepends on parameters which are frequently unknown, particularly thevalue of the coefficient of friction between the tyre and the ground.

The applicant has perceived that the deformed carcass profile, at agiven inflation pressure, itself yields a description of the actualbehaviour of the tyre in motion. Other significant parameters for theinterpretation of the measurements of the deformations of the tyre arethe value of the inflation pressure of the tyre, the temperature of thefluid within the tyre, and its velocity or acceleration.

The deformations of the carcass profile considered for the purposes ofthe present invention are defined as follows:

-   -   flattening (X₁): the deformation directed along a vertical axis        or in any case along an axis perpendicular to the road surface;    -   lateral displacement, or skidding, or drift (X₂): the        deformation directed along the axis of rotation of the tyre;    -   longitudinal creep or torsion (X₃): the deformation directed        along the circumferential direction, in other words the        direction of rolling of the tyre.

A more detailed description of the relations present between the saidvalues and the behaviour of a tyre is given in the aforesaid patentapplication 99EP-114962.6 in the name of the present applicant.

The measurement of these deformations is expressed as a variation of X₁,X₂, X₃ with respect to corresponding values determined on theequilibrium profile of the tyre at a specific inflation pressure.

The inner surface of the tyre, particularly the component called the“liner”, interacts with the sensor 11 in the determination of X₁, X₂,and X₃ as shown in FIGS. 9, 10, and 11.

In FIG. 9, the distance X₁ corresponds to the distance between thesurface of the liner 111 and the sensor 11 in the direction of theradius of rolling of the tyre.

In FIG. 10, the distance X₂ corresponds to the displacement in thetransverse direction of the point of projection of the sensor 11 on thesurface of the liner 111 with respect to the point of intersection ofthe surface of the liner with the equatorial plane E.

In FIG. 11, the distance X₃ corresponds to the displacement in thecircumferential direction of the point of projection of the sensor 11 onthe surface of the liner 111, along the equatorial plane, with respectto the point of the surface of the liner in the centre of the footprintarea.

For the purpose of measuring these distances, the sensor 11 emits asignal which is reflected from the liner with an intensity which differsaccording to its position with respect to the sensor. The reflectiontime of the signal can be measured in combination with the measurementof the intensity, or as an alternative to it. The reflected signalreceived by the sensor is suitably encoded according to the angle ofreflection and/or the differences of intensity and/or reflection timefrom predetermined values, in such a way as to determine the value ofX₁, X₂ and X₃.

Advantageously, the reflected signals can be encoded in the sensoritself. For example, the sensor can emit two optical beams, eachdirected towards a predetermined point on the surface of the liner.

In FIG. 10, a first optical beam is directed towards a point S₁ on thesidewall 10 of the tyre, and a second optical beam is directed towards apoint S₂ of the opposite sidewall 10′. The optical beams are orientatedin such a way that the points S₁ and S₂ are on the same horizontalplane. Each of the two measured distances represents the distance of thesensor 11 from the corresponding sidewall in the direction of theoptical beam which is emitted. X₂ can be calculated by comparing themeasurements of these two distances with each other, if the angles ofemission of the optical beams are known.

FIG. 12, which illustrates the bean-shaped deformation of the footprintarea of the tyre during drifting, depicting the paths of the bead wires6, 6′ and the mid-line k of the tread, shows how X₂ varies with theposition, with respect to the said area, of the cross section (radialplanes r₁, r₂, r₃, r₄) on which the determination is carried out, movingfrom the value t₁ to t₂, then to t₃ and finally to t_(n), along thelongitudinal extension of the footprint area. This variation can bemeasured by a series of successive determinations which are distributedover a period of time or distributed circumferentially along the saidlongitudinal extension.

In FIG. 11, a first optical beam is directed towards a point Y₁ on thesurface of the liner on the equatorial plane of the tyre. This point Y₁is close to the start of the footprint area in the direction of advanceof the tyre. A second optical beam is directed towards a point Y₂ on thesurface of the liner on the equatorial plane of the tyre. This point isclose to the exit from the footprint area, in other words in thedirection opposite the direction of advance of the tyre. Additionally,the optical beams are orientated in such a way that the points Y₁ and Y₂are on the same horizontal plane.

Each of the two measured distances represents the distance of the sensor11 from the corresponding point Y₁ or Y₂ in the direction of the emittedoptical beam.

X₃ can be calculated by comparing the measurements of these twodistances with each other, if the angles of emission of the opticalbeams are known.

Alternatively, instead of measuring the distance between two points, thesensor may carry out an integration of different determinations betweenadjacent points, thus reconstructing the shape of an extended portion ofthe inner surface of the tyre.

It should be understood that the sensor and the reflecting elementdescribed above can be replaced with equivalent effect, within the scopeof the present invention, with other types of sensors and reflectingelements capable of determining the aforesaid parameters by thereflection of a signal within the tyre.

Alternatively, it is possible to mount a plurality of sensors on therim, these sensors being preferably located in positions equidistantfrom each other, in such a way as to maintain a uniform distribution ofthe masses in the wheel, and each sensor being capable of measuring onlyone characteristic distance. Moreover, the number of the sensors may besuch as to permit the determination of each characteristic value morethan once during a complete rotation of the wheel. Preferably, thenumber of fixed coils located on the hub is equal to the number ofsensors located on the rim.

Alternatively, a single sensor may be capable of measuring X₁, X₂ and X₃simultaneously and sending, for example, a signal consisting of a firstamplitude modulation for X₁ in a first time interval, a second amplitudemodulation for X₂ in a second time interval, and a third amplitudemodulation for X₃ in a third time interval. The set of three timeintervals lies within the time interval used for the measurement.

The system of monitoring the deformed profile of the tyre preferablyalso comprises a pressure measuring device and/or a velocity and/oracceleration measuring device.

Alternatively, the moving station can be self-powered, using batterieslocated within it, a suitable timer enabling the measurement of thecharacteristic distances, preferably at the moment of the passage of thesensor under the footprint area of the tyre.

In a different embodiment, communication between the moving station andthe fixed station is provided by means of radio waves, by including asuitable transmitter in the moving station and a suitable receiver inthe fixed station.

The moving station is advantageously associated with the rim of thetyre, which forms an essential component for the determination of thedeformations of the tyre. It should be noted that the rim has normallybeen used only as the support for mounting devices capable ofdetermining the pressure and/or temperature within the tyre, and has nothad any significance in relation to the determination of thedeformations of the tyre, and of the tread in particular. In the systemof determining the deformations according to the invention, the rimbecomes the reference element, being the zero point, or in other wordsthe centre of the system of Cartesian axes in which the dimensionalvariations of the tyre are measured in the three directions. The choiceof the rim as the reference base is particularly advantageous becausethe rim is a rigid component of the pneumatic wheel, and is thereforeessentially free of dimensional variations in its structure during therotation of the tyre. In other words, the rigidity of the rim is thecharacteristic which allows it to be chosen as the fixed reference pointon which the measurements made are based. Additionally, the surface ofthe rim permits easy access to the inner cavity of the tyre, thusfacilitating the determination of the deformations within the tyre.

Example of Measurement

The method of determining a specific value in a tyre produced by thepresent applicant is described, purely by way of example, with referenceto FIGS. 7 a and 7 b. In particular, the value to be measured is theflattening X₁, corresponding to the distance d in FIG. 7 a, in a tyre ofthe 195/65R15 type, speed class V, in other words up to 240 km/hr,inflated to a pressure of 2.2 bars.

The distance d to be measured is of the order of 60 mm, the distance bis approximately 15 mm and the distance d₁ is approximately 9 mm.

For each millimetre of variation of the distance d, in other words ofthe flattening X₁, a value s−s₀ of approximately 40 μm is found. Thisvalue determines the sensitivity to displacement which the pair ofdiodes must have in order to determine variations of the distance d ofthe order of a millimetre.

The power supply to the fixed station is provided by the vehiclebattery, at a voltage of 12 volts in particular, and the frequency ofthe power supply signal to the fixed coil is chosen to be approximately1 MHz.

The maximum rotation velocity of the tyre may be 2500 r.p.m., and themeasurement is to be made at this velocity. A fixed coil with a diameterof approximately 10 cm and a moving coil with a diameter ofapproximately 2 cm are chosen, with a gap of approximately 7 mm betweenthe two coils. With a fixed coil of elliptical shape, the arc alongwhich the two coils are completely facing each other is approximately 12cm long. At a velocity of 2500 r.p.m., the useful measurement interval,in other words that in which the moving coil is acted on by the magneticfield generated by the fixed coil, is approximately 720 μs.

The power supply circuit 32 of the moving station 30 is designed in sucha way that there is a charge time of not more than 100 μs. In the next200 μs, the LED, being correctly powered, emits an optical beam ofinfrared light.

In the next 100 μs, the optical beam emitted by the LED is reflectedfrom the surface of the tyre and captured by the pair of p-i-n diodes,after which the reading circuit 37 reads the determination received fromthe said pair of diodes.

The total darkness present in the cavity of the tyre facilitates thereflection of the optical beam and its reception by the p-i-n diodes.The quantity of light which is reflected from the surface of the tyre isapproximately 10% of the quantity of light emitted by the LED; thequantity of light received by the pair of p-i-n diodes is approximately10% of the quantity of light reflected from the surface of the tyre. Theemission power of the LED is approximately 1.5 mW, and therefore thetotal optical power received by the p-i-n diodes is approximately 1.5μW. The sensitivity of the p-i-n diodes used is approximately 0.5 A/W,and therefore the current generated by the said diodes is approximately0.75 μA.

The quantity of light emitted by the LED can conveniently be controlledby varying the power of the supply circuit 32, in such a way as toenable the p-i-n diodes to receive an optimal quantity of light.

During the final 200 μs of the time period used for making themeasurement, the signal emitted by the reading circuit is transmitted tothe fixed station by means of the antenna, and separated from thecarrier wave in the fixed station by means of the demodulator 27.

Preferably, a computer installed on board the vehicle interprets thereceived signal, makes it available to the user in an understandablelanguage, activates any information or alarm devices, and uses it toactivate any automatic devices for controlling the attitude of thevehicle.

Finally, the attention of the skilled person is drawn to the fact thatthe moving station, in the described embodiment, takes the form of acylinder with a height of several centimetres. Since this cylinderprojects radially from the surface of the rim towards the interior ofthe wheel cavity, it forms an element interfering with the beads of thetyre during the stage of fitting the said tyre on the rim. In otherwords, the moving stations do not allow the beads to slide axially alongthe surface of the rim until they reach the corresponding bead seats andbear on the flanges of the rim.

The moving stations must therefore be removed during the operation offitting the tyre on the rim: in practice, the stage of fitting a tyre ona rim designed to house at least one moving station according to thepresent invention is carried out in the following stages:

-   -   an airtight sealing element is inserted in each hole present on        the rim for housing the moving stations, this element generally        being a screw plug interchangeable with the said station;    -   the tyre is fitted on the rim by making the beads of the tyre        pass in succession over the same flange of the rim and bringing        the said beads to the start of the conical surfaces which        axially delimit the inner edges of the bead seats;    -   pressurized air is admitted to the tyre in such a way that each        bead is brought on to the corresponding bead seat, and bears on        the said flanges located at the axially opposite edges of the        rim;    -   the tyre is deflated and the sealing elements are replaced with        the moving stations;    -   the tyre is inflated to the desired pressure.

The sealing elements are only required to ensure air-tightness, to allowthe beads to be forced into the corresponding seats, and therefore theydo not need to project radially into the cavity of the tyre: thus theyallow the beads of the tyre to slide easily over the surface of the rimuntil they reach the specified fitting position.

1. A system for monitoring deformations of a moving tyre mounted on arim associated with a vehicle, comprising: a moving station; and a fixedstation; wherein the moving station is operatively coupled to the rim,wherein the moving station measures, at least intermittently and atleast one direction, a distance between the moving station and an innersurface of the tyre, wherein the fixed station is operatively coupled tothe vehicle, wherein the fixed station receives from the moving station,at least intermittently, at least one first signal associated with themeasurement, and wherein the moving station measures the distance withina time interval when a first antenna associated with the moving stationand a second antenna associated with the fixed station are in proximityto each other.
 2. The system of claim 1, wherein the moving stationcomprises at least one first sensor that transmits, at leastintermittently, at least one second signal within the tyre in apredetermined direction, and receives one or more reflections of the atleast one second signal from the inner surface of the tyre.
 3. Thesystem of claim 2, wherein the at least one second signal comprises oneor more sound waves.
 4. The system of claim 2, wherein the at least onesecond signal comprises one or more optical beams.
 5. The system ofclaim 2, wherein the at least one second signal comprises one or moreelectromagnetic waves.
 6. The system of claim 2, wherein the at leastone first sensor comprises a first electronic circuit board, and whereinthe first electronic circuit board comprises: a beam emitting device;and a beam receiving device.
 7. The system of claim 6, wherein the firstelectronic circuit board comprises: the first antenna; a power-supplyunit; a drive circuit for the beam emitting device; a drive circuit forthe beam receiving device; and a circuit for reading at least one thirdsignal from the beam receiving device; wherein the first antenna iselectrically connected to the power-supply unit, wherein thepower-supply unit supplies power to the drive circuit or the beamemitting device, and wherein the power-supply unit supplies power to thedrive circuit or the beam receiving device.
 8. The system of claim 2,wherein the at least one first sensor comprises a first electroniccircuit board, and wherein the first electronic circuit board comprises:a beam emitting device; a first lens; a second lens; and a beamreceiving device.
 9. The system of claim 8, wherein the first electroniccircuit board comprises: the first antenna; a power-supply unit; a drivecircuit for the beam emitting device; a drive circuit for the beamreceiving device; and a circuit for reading at least one third signalfrom the beam receiving device; wherein the first antenna iselectrically connected to the power-supply unit, wherein thepower-supply unit supplies power to the drive circuit for the beamemitting device, and wherein the power-supply unit supplies power to thedrive circuit or the beam receiving device.
 10. The system of claim 2,wherein the at least one first sensor comprises a first electroniccircuit board, and wherein the first electronic circuit board comprises:an optical-beam emitting device; a first lens; a second lens; and anoptical-beam receiving device.
 11. The system of claim 10, wherein thefirst electronic circuit board comprises: the first antenna; apower-supply unit; a drive circuit for the optical-beam emitting device;a drive circuit for the optical-beam receiving device; and a circuit forreading at least one third signal from the optical-beam receivingdevice; wherein the first antenna is electrically connected to thepower-supply unit, wherein the power-supply unit supplies power to thedrive circuit for the optical-beam emitting device, and wherein thepower-supply unit supplies power to the drive circuit for theoptical-beam receiving device.
 12. The system of claim 10, wherein theoptical-beam emitting device comprises a light-emitting diode (LED). 13.The system of claim 10, wherein the optical-beam receiving devicecomprises a pair of p-i-n diodes.
 14. The system of claim 1, wherein themoving station comprises at least one first sensor that transmits, atleast intermittently, at least one second signal within the tyre in apredetermined direction, and wherein the moving station furthercomprises at least one second sensor that receives one or morereflections of the at least one second signal from the inner surface ofthe tyre.
 15. The system of claim 14, wherein the at least one secondsignal comprises one or more sound waves.
 16. The system of claim 14,wherein the at least one second signal comprises one or more opticalbeams.
 17. The system of claim 14, wherein the at least one secondsignal comprises one or more electromagnetic waves.
 18. The system ofclaim 14, wherein the at least one first sensor comprises a firstelectronic circuit board, and wherein the first electronic circuit boardcomprises: a beam emitting device; and a beam receiving device.
 19. Thesystem of claim 18, wherein the first electronic circuit boardcomprises: the first antenna; a power-supply unit; a drive circuit forthe beam emitting device; a drive circuit for the beam receiving device;and a circuit for reading at least one third signal from the beamreceiving device; wherein the first antenna is electrically connected tothe power-supply unit, wherein the power-supply unit supplies power tothe drive circuit for the beam emitting device, and wherein thepower-supply unit supplies power to the drive circuit for the beamreceiving device.
 20. The system of claim 14, wherein the at least onefirst sensor comprises a first electronic circuit board, and wherein thefirst electronic circuit board comprises: a beam emitting device; afirst lens; a second lens; and a beam receiving device.
 21. The systemof claim 20, wherein the first electronic circuit board comprises: thefirst antenna; a power-supply unit; a drive circuit for the beamemitting device; a drive circuit for the beam receiving device; and acircuit for reading at least one third signal from the beam receivingdevice; wherein the first antenna is electrically connected to thepower-supply unit, wherein the power-supply unit supplies power to thedrive circuit for the beam emitting device, and wherein the power-supplyunit supplies power to the drive circuit for the beam receiving device.22. The system of claim 14, wherein the at least one first sensorcomprises a first electronic circuit board, and wherein the firstelectronic circuit board comprises: an optical-beam emitting device; afirst lens; a second lens; and an optical-beam receiving device.
 23. Thesystem of claim 22, wherein the first electronic circuit boardcomprises: the first antenna; a power-supply unit; a drive circuit forthe optical-beam emitting device; a drive circuit for the optical-beamreceiving device; and a circuit for reading at least one third signalfrom the optical-beam receiving device; wherein the first antenna iselectrically connected to the power-supply unit, wherein thepower-supply unit supplies power to the drive circuit for theoptical-beam emitting device, and wherein the power-supply unit suppliespower to the drive circuit for the optical-beam receiving device. 24.The system of claim 22, wherein the optical-beam emitting devicecomprises an LED.
 25. The system of claim 22, wherein the optical-beamdevice comprises a pair of p-i-n diodes.
 26. The system of claim 1,wherein the fixed station enables the moving station to measure thedistance.
 27. The system of claim 1, wherein the at least one firstsignal comprises a processed signal.
 28. The system of claim 1, whereinthe fixed station is powered by a battery of the vehicle.
 29. A methodfor monitoring deformations of a moving tyre mounted on a rim associatedwith a vehicle, comprising the steps of: enabling a moving station tomeasure, at least intermittently and in at least one direction, adistance between the moving station and an inner surface of the tyre;and transmitting at least one signal associated with the measurementfrom the moving station; and receiving the at least one signal at afixed station; wherein the moving station is operatively coupled to therim, wherein the fixed station is operatively coupled to the vehicle,and wherein the moving station measures the distance within a timeinterval when a first antenna associated with the moving station and asecond antenna associated with the fixed station are in proximity toeach other.
 30. The method of claim 29, further comprising the step ofprocessing information associated with the measurement beforetransmitting the at least one signal from the moving station to thefixed station.
 31. The method of claim 29, wherein the step of enablingthe moving station comprises measuring the distance when the movingstation is in a proximity of a footprint area of the tyre.
 32. Themethod of claim 29, wherein the steps of enabling the moving station andtransmitting the at least one signal occur within the time interval whenthe first antenna and the second antenna are in proximity to each other.33. The method of claim 29, wherein the step of enabling the movingstation comprises supplying power to the moving station when the movingstation is in a proximity of a footprint area of the tyre.
 34. Themethod of claim 29, wherein the step of enabling the moving stationcomprises supplying power to the moving station within the time intervalwhen the first antenna and the second antenna are in proximity to eachother.
 35. The method of claim 29, wherein the step of transmitting theat least one signal comprises generating a magnetic field correspondingto the at least one signal in a proximity of the first antenna.
 36. Themethod of claim 29, wherein the step of receiving the at least onesignal comprises detecting a magnetic field corresponding to the atleast one signal in a proximity of the second antenna.
 37. A method formonitoring deformations of a moving tyre mounted on a rim associatedwith a vehicle, comprising the steps of: enabling a moving station totransmit at least one first signal when the moving station is in aproximity of a footprint area of the tyre; transmitting the at least onefirst signal, at least intermittently and in at least one direction,within the tyre; reflecting the at least one first signal from an innersurface of the tyre; receiving the reflected at least one first signal;and processing information associated with the reflected at least onefirst signal to measure a distance between the moving station and theinner surface of the tyre; wherein the moving station is operativelycoupled to the rim.
 38. The method of claim 37, further comprising thestep of: transmitting at least one second signal associated with themeasurement from the moving station; and receiving the at least onesecond signal at a fixed station; wherein the fixed station isoperatively coupled to the vehicle.
 39. The method of claim 38, whereinthe step of processing information occurs before the step oftransmitting the at least one second signal.
 40. The method of claim 38,wherein the step of processing information occurs after the step ofreceiving the at least one second signal.
 41. The method of claim 38,wherein the steps of enabling the moving station, transmitting the atleast one first signal, reflecting the at least one first signal,receiving the reflected at least one first signal, transmitting the atleast one second signal, and receiving the at least one second signaloccur when the moving station is in the proximity of the footprint areaof the tyre.
 42. The method of claim 38, wherein the steps of enablingthe moving station, transmitting the at least one first signal,reflecting the at least one first signal, receiving the reflected atleast one first signal, transmitting the at least one second signal, andreceiving the at least one second signal occur within a time intervalwhen a first antenna associated with the moving station and a secondantenna associated with the fixed station are in proximity to eachother.
 43. The method of claim 38, wherein the step of receiving the atleast one second signal comprises detecting a magnetic fieldcorresponding to the at least one second signal in a proximity of asecond antenna associated with the fixed station.
 44. The method ofclaim 37, wherein the steps of enabling the moving station, transmittingthe at least one first signal, reflecting the at least one first signal,and receiving the reflected at least one first signal occur when themoving station is in the proximity of the footprint area of the tyre.45. The method of claim 37, wherein the steps of enabling the movingstation, transmitting the at least one first signal, reflecting the atleast one first signal, and receiving the reflected at least one firstsignal occur within a time interval when a first antenna associated withthe moving station and a second antenna associated with a fixed stationare in proximity to each other.
 46. The method of claim 37, wherein thestep of enabling the moving station comprises supplying power to themoving station when the moving station is in the proximity of thefootprint area of the tyre.
 47. The method of claim 37, wherein the stepof enabling the moving station comprises supplying power to the movingstation within a time interval when a first antenna associated with themoving station and a second antenna associated with a fixed station arein proximity to each other.
 48. The method of claim 38, wherein the stepof transmitting the at least one second signal comprises generating amagnetic field corresponding to the at least one second signal in aproximity of a first antenna associated with the moving station.